This invention relates to a packaging machine of the so-called form-fill-seal type adapted to concurrently form a bag from a film, to fill it with articles and to seal it to obtain individual packaged products. More particularly, this invention relates to a method of and a device for adjusting the position on the film at which it is cut (xe2x80x9ccut-positionxe2x80x9d) to produce separated bags. The invention also relates to a packaging machine adapted to automatically adjust the cut-position according to an inputted size of the bags to be produced.
Packaging machines adapted to concurrently bend a film into a tubular form, to fill it with articles to be packaged and to clamp it between a pair of sealing members (xe2x80x9cseal jawsxe2x80x9d) to simultaneously seal the top part of a filled bag and the bottom of the next bag to be filled have been known. If the bags are formed from a film with a design printed thereon corresponding to each bag to be formed, marks (hereinafter referred to as the xe2x80x9ceye marksxe2x80x9d) which are detectable by a light sensor are printed on the film at longitudinal intervals corresponding to the length of the bags to be made such that the film can be accurately sealed over and cut at boundary areas between portions of the film corresponding to two mutually adjacent bags as the packaging machine is operated to repeat a cyclic motion.
Prior art methods of determining the cut-position of the bags or the clamping position by seal jaws can be roughly divided into those of adjusting the interval between the time when an eye mark on the film as a reference is detected and the time at which the film is cut (such as adjusting the dislocation of the cut-position while changing the time set on a timer by operating a dial) and those of displacing the position of the sensor for the eye marks (that is, to move the eye mark sensor by a distance corresponding to the displacement of the cut-position). The methods of the former kind are not desirable because repeated trials and errors tend to increase the wasted amount of the film. The methods of the latter kind are advantageous in that one has only to displace the eye mark sensor but it is a cumbersome operation to make the position adjustment while watching the markings of a dial.
In the case of packaging machines of a continuously operated type having a linearly moving transverse sealing mechanism, in particular, the cut-position of the film also changes whenever the stripping distance is changed according to the kind of the articles to be packaged or the pattern of motion (such as the time of sealing) for the transverse seal jaws. Thus, the operator had to adjust the cut-position whenever such a change had to be made. This also contributed to increase the waste of the film material.
It is therefore an object of this invention to provide an improved method of and a device for automatically adjusting the cut-position of a bag-making film material in response simply to an input of a displacement of the cut-position obtained from a dummy bag formed for testing.
It is also an object of this invention to provide a packaging machine incorporating such a device or method.
It is another object of this invention to provide a packaging machine capable of cutting the film automatically at intended positions in response only to an input of the bag size or the eye mark position.
It is a further object of this invention to provide a method of and a device for a packaging machine for automatically adjusting the cut-position of a bag-making film merely by transporting the film until a cut-position on the film reaches the film-cutting position.
According to a method embodying this invention, the motion of a pair of seal jaws is started after the film has been pulled over a specified length or for a specified length of time (both referred to as xe2x80x9cthe travel conditionxe2x80x9d) from the moment when an eye mark on the film is detected by a detector to thereby obtain a dummy bag for examining whether the film was cut at a right position. If not, the displacement from the intended cut-position is measured and used to correct the initially specified travel condition. Alternatively, the correction of the initially specified travel condition may be effected on the basis of displacement of the clamping position due to changes in various parameters for determining the pattern of the motion of the seal jaws.
A device embodying this invention may be characterized as comprising a memory for storing the aforementioned travel condition such as the distance by which the film is initially caused to travel between the time when an eye mark on the film is detected and the time when the motion of the seal jaws is to be started, an input means through which the displacement of the position on the film where it is actually cut and the intended cut-position is inputted, and calculating means for adjusting the aforementioned travel condition according to the displacement inputted through the input means.
A packaging machine of this invention may be characterized as comprising film transporting means such as pull-down belts for moving a film along a specified path, a detector for detecting an eye mark on the film, a transverse sealer operating cyclically and having a pair of seal jaws for clamping the film from opposite sides and cutting it to form a bag, a memory for storing certain data such as desired length of the bags to be made, and means for using these data to calculate a distance or time of travel by the film and controlling the motion of the seal jaws and hence the timing of clamping the film thereby.
Since the initial motion of the film (expressed either by the distance or time of its travel) is corrected by preliminarily producing a dummy bag as a test and measuring the displacement of the actually cut position from where the cutting was intended, the film-cutting position can be automatically and easily adjusted without wasting a large amount of film.
According to another method embodying this invention, the distance of travel by the film is measured from the moment when an eye mark is detected until the cut-position fixed on the film reaches the specified clamping position of the seal jaws and the timing of motion for the seal jaws at their initial positions is determined on the basis of this measured distance of travel. Accordingly, an adjusting device employing this method of adjustment may be characterized as comprising means for measuring and storing the distance of travel by the film from the detection of an eye mark until the cut-position reaches the clamping position and means for calculating the timing for starting the motion of seal jaws at their initial positions. With such a method or a device, the film can be cut exactly at the intended cut-position and hence the waste of the film can be reduced to a minimum merely by measuring the distance of travel of the film from the detection of an eye mark until the cut-position reaches the clamping position of the seal jaws.